Description: Ancient chambered tomb or Cromlech in Carmarthenshire , South Wales . GWAL Y FILIAST aka Bwrdd Arthur . Built about 3 , 500 years ago it is located on a steep wooded ridge overlooking the River Taff where the river changes character from slow flowing to rapids . The large capstone pointing towards the river to the west is supported by four uprights . The tomb would once have been covered by an oval or circular mound some kerbstones remain .